CCP

The complement control protein (CCP) modules (also known as short consensus repeats SCRs or SUSHI repeats) contain approximately 60 amino acid residues and have been identified in several proteins of the complement system. A missense mutation in seventh CCP domain causes deficiency of the b subunit of factor XIII.

The extracellular sushi domain is characterised by a consensus sequence spanning ~60 residues containing four invariant cysteine residues forming two disulfide-bridges (I-III and II-IV), a highly conserved tryptophan, and conserved glycine, proline, and hydrophobic residues [(PUBMED:2751824)]. Sushi domains are known to be involved in many recognition processes, including the binding of several complement factors to fragments C3b and C4b [(PUBMED:2751824)]. The sushi domain is also known as the complement controle protein (CCP) module or the short consensus repeat (SCR).

Several structure of the sushi domain have been solved (see for example {PDB:1HCC}) [(PUBMED:1829116)]. The sushi domain folds into a small and compact hydrophobic core enveloped by six beta-strands and stabilised by two disulfide bridges. The relative structural orientation of the Beta-2 and Beta-4 strands is shared by all the sushi structures, whereas the topology of the other strands relative to this central conserved core is variable, especially at the regions that form the interfaces with the preceding and following domains [(PUBMED:10775260)].

Molecular and cellular basis of deficiency of the b subunit for factor XIII secondary to a Cys430-Phe mutation in the seventh Sushi domain.

J Clin Invest. 1995; 95: 1002-8

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We studied the defect responsible for deficiency of the b subunit for factor XIII in the first known case of this condition. The patient is a compound heterozygote of two genetic defects: deletion of A-4161 at the acceptor splice junction of intron A, resulting in a loss of the obligatory AG splicing sequence; and, replacement of G-11499 by T in exon VIII, resulting in an amino acid substitution of Cys430 by Phe. To determine how the latter mutation impaired b subunit synthesis, recombinant b subunit bearing the mutation was expressed in BHK cells. The mutant as well as wild-type b subunit was synthesized by the cells. However, the apparent molecular weight of the mutant was slightly higher than those of the wild-type and plasma b subunits under nonreducing conditions, probably because of destruction of a disulfide bond. The mutant b subunit was secreted from the cells much less effectively than the wild type and remained susceptible to endoglycosidase H, indicating that it was not transported from the endoplasmic reticulum to the Golgi apparatus where the processing of oligosaccharides occurs. Immunofluorescence study suggested that the mutant protein was retained in the endoplasmic reticulum. These studies demonstrate that a Cys430-Phe mutation does not prevent the de novo synthesis of the b subunit, but alters the conformation of the mutant protein sufficiently to impair its intracellular transport, resulting in its deficiency in this patient.

Three-dimensional structure of a complement control protein module in solution.

J Mol Biol. 1991; 219: 717-25

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The complement control protein (CCP) modules (also known as short consensus repeats) are defined by a consensus sequence within a stretch of about 60 amino acid residues. These modules have been identified more than 140 times in over 20 proteins, including 12 proteins of the complement system. The solution structure of the 16th CCP module from human complement factor H has been determined by a combination of 2-dimensional nuclear magnetic resonance spectroscopy and restrained simulated annealing. In all, 548 structurally important nuclear Overhauser enhancement cross-peaks were quantified as distance restraints and, together with 41 experimentally measured angle restraints, were incorporated into a simulated annealing protocol to determine a family of closely related structures that satisfied the experimental observations. The CCP structure is shown to be based on a beta-sandwich arrangement; one face made up of three beta-strands hydrogen-bonded to form a triple-stranded region at its centre and the other face formed from two separate beta-strands. Both faces of the molecule contribute highly conserved hydrophobic side-chains to a compact core. The regions between the beta-strands are composed of both well-defined turns and less well-defined loops. Analysis of CCP sequence alignments, in light of the determined structure, reveals a high degree of conservation amongst residues of obvious structural importance, while almost all insertions, deletions or replacements observed in the known sequences are found in the less well-defined loop regions. On the basis of these observations it is postulated that models of other CCP modules that are based on the structure presented here will be accurate. Certain families of CCP modules differ from the consensus in that they contain extra cysteine residues. As a test of structural consensus, the extra disulphide bridges are shown to be easily accommodated within the determined CCP model.

The complete amino acid sequence of the human complement system regulatory protein, factor H, has been derived from sequencing three overlapping cDNA clones. The sequence consists of 1213 amino acids arranged in 20 homologous units, each about 60 amino acids long, and an 18-residue leader sequence. The 60-amino-acid-long repetitive units are homologous with those found in a large number of other complement and non-complement proteins. Two basic C-terminal residues, deduced from the cDNA sequence, are absent from factor H isolated from outdated plasma. A tyrosine/histidine polymorphism was observed within the seventh homologous repeat unit of factor H. This is likely to represent a difference between the two major allelic variants of factor H. The nature of the cDNA clones indicates that there is likely to be an alternative splicing mechanism, resulting in the formation of at least two species of factor H mRNA.

Disease (disease genes where sequence variants are found in this domain)

This information is based on mapping of SMART genomic protein database to KEGG orthologous groups. Percentage points are related to the number of proteins with CCP domain which could be assigned to a KEGG orthologous group, and not all proteins containing CCP domain. Please note that proteins can be included in multiple pathways, ie. the numbers above will not always add up to 100%.